Dynamoelectric machines such as the large electrical generators manufactured by Westinghouse Electric Company include multiple phase windings, which are positioned in slots in a laminated magnetic core. In such a generator, the movement of a rotor about an axis shifts a magnetic field which is associated with the rotor, thereby inducing a current to flow through each of the respective phase windings. Unfortunately, the convergence of magnetic flux from the rotor and from the windings themselves can cause additional induced voltage and eddy currents in the respective phase windings. Similar fluxes affect the end region or involute portions of the phase windings outside the slots. For this reason, the phase windings of large electrical generators are always of stranded construction, being built up of a substantial number of relatively thin strands to minimize the eddy current loss. The fluxes, however, are not uniform, but vary radially in density. The induced voltage thus varies from strand to strand, thereby causing excessive losses and heating if left untreated. To ameliorate this effect, it is common to transpose the strands in order to cancel out the unbalanced strand voltages. This tends to minimize the circulating currents and resultant heating. The most common type of transposition is that disclosed in U.S. Pat. No. 1,144,252 to Roebel.
In the stator of a gas inner-cooled electrodynamic power generator, coils are constructed of columns or stacks of copper strands and stacks of vent tubes, through which a coolant such as hydrogen gas is circulated. FIG. 1 is a cross-sectional view through a half-coil 10 of such a gas inner-cooled stator winding shown positioned in a slot of a stator 11. As may be seen in FIG. 1, the half-coil 10 includes a tube stack 12 of tubes 14 for circulating a coolant, wit of strand stacks 16, 18 and 20, 22, respectively, positioned on each side of the tube stack 12. Each of the strand stacks 16, 18, 20, 22 contain a plurality of individual strands 24, which are electrically insulated from each other and have a substantially rectangular cross-section to facilitate stacking. In such a half-coil 10, it is usual to transpose strand stack 16 with strand stack 18 and to transpose strand stack 20 with strand stack 22 to cancel out as far as possible the unbalanced voltages which might otherwise be generated between strands in the respective stacks.
Certain electrodynamic machinery requires more than one tube stack for conducting heat away from a half-coil of a stator winding. FIGS. 2 and 3 depict a half-coil configuration 26 which has been used in the past by Westinghouse Electric Company, the assignee hereof, for double tube stack applications. As shown in the cross-sectional view provided in FIG. 2, half-coil 26 included a first tube stack 28 positioned between a first strand stack 30 and a second strand stack 32. The assembly consisting of first strand stack 30, first tube stack 28 and second strand stack 32 was positioned immediately adjacent to a second assembly formed by second tube stack 34, third strand stack 36 and fourth strand stack 38. FIG. 3 depicts the transpositions 42 which were made between the first and second strand stacks 30, 32 and the third and fourth strand stacks 36, 38, respectively. As may be seen in FIG. 3, those transpositions were made about the respective tube stacks 28, 34, resulting in the creation of large spaces or voids 40 between the strand stacks. The voids 40 were two stacks in depth in some places, and tended to form an open chevron pattern along the length of the half-coil. To eliminate corona discharges within the coil insulation, it was necessary to fill the voids 40 with a dielectric material such as an impregnated dacron batting. This process, as might be imagined was extremely labor intensive. Moreover, the relative lack of density in the half-coil 26 that was caused by the voids 40 adversely affected the performance of the electrodynamic machinery.
To form a continuous coil, the various half-coils in an electrodynamic motor or generator are electrically connected at the end or involute portions of the slots. In the past, the half-coil ends were separated into specified groups of strands, which were cleaned, tinned, bundled into clips and soldered into series connectors to minimize power loss. This process was also labor intensive, time consuming and cumbersome.
It is clear that there has existed and long a unfilled need in the prior art for a half-coil configuration for use within the stator of an electrodynamic machine such as an electrical generator which includes more than one stack of cooling tubes, which achieves higher strand density with fewer void areas than was heretofore possible, and which is less labor intensive to install than those methods and systems heretofore known.